Input fell dreadfully; it's quite common (9)
I believe the answer is:
plentiful
'quite common' is the definition.
'plentiful' can be an answer for 'common' (I've seen this before). I'm unsure of the 'quite' bit.
'input fell dreadfully' is the wordplay.
'dreadfully' indicates an anagram (a dreadful spelling).
'input'+'fell'='inputfell'
'inputfell' with letters rearranged gives 'PLENTIFUL'.
'it's' is the link.
Can you help me to learn more?
(Other definitions for plentiful that I've seen before include "Abundant, copious" , "Productive" , "Existing in great quantities" , "common" , "Abundant - profuse" .)